[LTP] [PATCH v2] io: fix really slow dio_sparse on certain systems

[Andrea Cervesato]

From: Andrea Cervesato <andrea.cervesato@suse.com>

The reason why dio_sparse is happening to be slow on certain systems is
that, if data buffering is slow, we run more buffered read() for one
single dio write(). This slows down the whole test, because for each
read() we always need to move data from kernel space to user space.

Create a READ_BUFFER_SIZE variable inside the common.h header and use
it to define the write buffer size.

Signed-off-by: Andrea Cervesato <andrea.cervesato@suse.com>
---
Changes in v2:
- fix write option default value in the documentation
- Link to v1: https://lore.kernel.org/r/20260123-fix_dio_sparse_slow-v1-1-65bd0dc0d52f@suse.com
---
 testcases/kernel/io/ltp-aiodio/common.h     | 6 ++++--
 testcases/kernel/io/ltp-aiodio/dio_sparse.c | 4 ++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/testcases/kernel/io/ltp-aiodio/common.h b/testcases/kernel/io/ltp-aiodio/common.h
index 9a2d2716661651adf40c635ac516cc70068c9393..d3f05a3c1e75cd4baa629cbce1872729a0d641c6 100644
--- a/testcases/kernel/io/ltp-aiodio/common.h
+++ b/testcases/kernel/io/ltp-aiodio/common.h
@@ -9,6 +9,8 @@
 #include <stdlib.h>
 #include "tst_test.h"
 
+#define READ_BUFFER_SIZE 4096
+
 static inline char *check_zero(char *buf, int size)
 {
 	char *p;
@@ -57,7 +59,7 @@ static inline void io_append(const char *path, char pattern, int flags, size_t b
 
 static inline void io_read(const char *filename, int filesize, volatile int *run_child)
 {
-	char buff[4096];
+	char buff[READ_BUFFER_SIZE];
 	int fd;
 	int i;
 	int r;
@@ -102,7 +104,7 @@ exit:
 
 static inline void io_read_eof(const char *filename, volatile int *run_child)
 {
-	char buff[4096];
+	char buff[READ_BUFFER_SIZE];
 	int fd;
 	int r;
 
diff --git a/testcases/kernel/io/ltp-aiodio/dio_sparse.c b/testcases/kernel/io/ltp-aiodio/dio_sparse.c
index c87e5ab1aca7c8910f76ee87f86b561f548d4cdf..4edf286420831cef5f4280e620651554182aaa52 100644
--- a/testcases/kernel/io/ltp-aiodio/dio_sparse.c
+++ b/testcases/kernel/io/ltp-aiodio/dio_sparse.c
@@ -32,7 +32,7 @@ static char *str_filesize;
 static char *str_offset;
 
 static int numchildren = 16;
-static long long writesize = 1024;
+static long long writesize = READ_BUFFER_SIZE;
 static long long filesize = 100 * 1024 * 1024;
 static long long offset = 0;
 static long long alignment;
@@ -124,7 +124,7 @@ static struct tst_test test = {
 	.forks_child = 1,
 	.options = (struct tst_option[]) {
 		{"n:", &str_numchildren, "Number of threads (default 16)"},
-		{"w:", &str_writesize, "Size of writing blocks (default 1K)"},
+		{"w:", &str_writesize, "Size of writing blocks (default 4K)"},
 		{"s:", &str_filesize, "Size of file (default 100M)"},
 		{"o:", &str_offset, "File offset (default 0)"},
 		{}

---
base-commit: c47ab95d5fe077133e598ac7762387450a87cb2b
change-id: 20260123-fix_dio_sparse_slow-925958767d74

Best regards,
-- 
Andrea Cervesato <andrea.cervesato@suse.com>